The aggregation of cholesterol in bile salts, model bile and real bile will be observed with hydrodynamic chromatography. The use of bile salt electrodes to monitor bile salt ion activities will be extended to model and real bile. More selective bile salt and fatty acid electrodes, which will respond only to the desired species, are under development, with the goal of measuring intestinal bile salt and fatty acid ion activities in vivo. The solubilization of liquid intestinal lipids in bile salt solutions will be measured with a newly-developed rising drop apparatus. It is planned that model and real bile will be observed by electron microscopy using polymeric cryoprotectants.